The invention relates to an arrangement for the damped bearing of a rotor shaft of an electric machine. The invention further relates to an electric machine comprising a rotor shaft and at least one such arrangement. The invention also relates to a method for the damped bearing of a rotor shaft of such an electric machine.
Such arrangements and such a method are used, for example, in electric motors or generators. If any type of rotor is mounted in a rotatable manner, depending on the type of bearing, natural frequencies are produced with the associated natural mode shapes. Rotor bearings may be designed, for example, as hydrodynamic plain bearings, hydrostatic plain bearings, rolling bearings, active and passive magnetic bearings or air bearings.
Here, a differentiation is made between subcritical rotors and supercritical rotors. If the principal natural frequency of the system is above its operating speed, then this is called a subcritical rotor. If the natural frequencies are below the operating speed, this is a supercritical rotor. In this case, a specific degree of external damping is required at the bearing points in order to be able to pass through the natural frequencies up to the operating speed or in order to be able to operate the rotor at its natural frequency. Moreover, it is possible that an instability of the rotor system occurs as a result of internal damping of the rotor or due to the carrier medium of plain bearings. In order to prevent this, external damping at the bearing points is also required.
In a rotor bearing with only a very small degree of external damping at the bearing points, it is not possible to operate the rotor supercritically. A type of bearing which only generates a small degree of damping is implemented, for example, a rolling bearing. In plain bearings, damping may be produced by the carrier medium. Frequently, however, this is not sufficiently high in order to operate the rotor in one of its natural frequencies and in order to be able to avoid instabilities in any rotational speed range. Passive magnetic bearings and air bearings also have only very low damping properties. In active magnetic bearings the rotor system is kept stable by external magnetic forces and damping of the bearing is produced.
If the damping at the bearing points is insufficient there are different options for producing additional damping, for example rubber elements below the bearing or squeeze film dampers below the bearing or directly on the rotor.
A bearing ring is disclosed in DE 197 01 178 A1 which has an inner bearing shell and an outer bearing shell which are arranged at a radial distance from one another, and an element which connects together the two bearing shells fixedly in terms of rotation and which is designed as a knitted wire fabric is arranged in the intermediate space thus formed within said bearing shells.
A rolling bearing having a very similar construction is disclosed in DE 10 2006 058 172 A1.
An axial rolling bearing which comprises an upper ring, a lower ring and balls between the rings is disclosed in DE 20 2010 004 482 U1, wherein a pressed strip made of metal fibers is used for the rings and wherein the rings are overmolded with plastic shells.